Many consumer and industrial products are formed from thermoplastic composite or laminate materials. Such materials include for example container walls and countertop materials. For a variety of aesthetic and functional reasons the composites or laminates may be composed of quite dissimilar polymers. For example, composite materials are often blends of two or more polymers that are present in discrete phases within the polymer matrix, due to the differing chemical properties of each polymeric component. Laminated materials often are designed to have particular barrier properties and contain plies made from dissimilar polymers. The polymeric materials of the various layers then act to transmit or prevent transmission of certain gases in a controlled manner. For example, a container lid or a fuel tank wall may be a laminated material that contains a polar polymer and a non-polar polymer in separate layers.
Some commonly used polymers that are present in laminated or composite materials include polyamides, polyolefins, polyesters and ethylene copolymers. Among this latter group are ethylene copolymers having polar comonomers, such as ethylene vinyl alcohol copolymers, ethylene acrylic acid copolymers and ethylene methacrylic acid copolymers. Recycling processes have the potential to convert such laminated or composite materials into useful raw materials, but in many cases the basic incompatibility of the polymers in the recyclable product leads to production of non-homogeneous blends that have unacceptable physical properties. One solution to this problem is the use of additives that compatibilize dissimilar polymers. For example, in U.S. Pat. No. 6,294,602 a process for recycling a mixture of ethylene vinyl alcohol copolymer and a thermoplastic resin using a compatibilizer that is a mixture of a polyamide resin and an ethylene-unsaturated carboxylic acid random copolymer or its metal salt is disclosed. Other compatibilizers are disclosed in K. Hausmann, “Compatibilizers, Polymeric (Recycling of Multilayer Structures)”, Polymeric Materials Encyclopedia, CRC Press, New York, 1996, vol. 2, pp. 1364-1377.
Maleated polymers are a useful class of compatibilizing agents and toughening agents for thermoplastic polymers. Such polymers include maleic anhydride-grafted polyolefins and ethylene copolymers having copolymerized monomer units of maleic acid, maleic acid esters or maleic anhydride. For example, U.S. Pat. No. 5,179,164 discloses molding compositions comprising polypropylenes, polyamides and ethylene copolymers grafted with maleic anhydride. PCT Published Application No. WO 98/41576 discloses toughened polyamides that are blends of ultrahigh density polyethylene, polyamide and maleic anhydride graft copolymers. In addition, U.S. Pat. Nos. 4,174,358 and 5,408,000 and PCT Published Application No. WO 03/099930A1 disclose various impact modifiers for polyamides that include maleated polymers.
Maleic anhydride grafted polyolefins are generally prepared on a commercial scale by grafting maleic anhydride onto a polymeric backbone material, such as polyethylene, polypropylene, styrene-ethylene-butene-styrene triblock copolymer or polybutadiene. Maleated compatibilizers of this type include, e.g. Fusabond® MB 226DE and Fusabond® MD 353D adhesive resins, available from E. I. du Pont de Nemours and Company. Another class of maleated compatibilizers includes ethylene dipolymers and higher order copolymers that contain copolymerized units of e.g. maleic acid.
Although maleated polymers have been used as compatibilizers for various resins, their potential as additives in recycling operations has not been fully utilized and optimized. It would be desirable to have a process available that makes more effective use of this class of compatibilizing agents in recycling processes. In addition, it would be useful to have a process available that could more effectively compatibilize dissimilar polymers made from virgin materials. Compositions produced by such processes would be economical raw materials for fabricating consumer and industrial goods.